Steam generator

ABSTRACT

A steam generator includes inverted U-shaped tubes having vertical legs and formed into two nests each having inlet and outlet groups of legs with the return portions of all of the tubes positioned in the lower portion of an enclosure having a steam outlet and in which a water separator for the generated steam is positioned above the tube return portions. Individual casings all connecting with the enclosure&#39;&#39;s lower portion, extended downwardly therefrom and individually encase the respective groups of legs individually, the ends of each group of legs being mounted in a tube sheet separate from the others. Each of these tube sheets is provided with a separate manifold for the tubes of the group of legs mounted by that tube sheet. This construction permits the use of tube sheets which are individually small while permitting the heat exchanger to be designed to have a relatively high steam generated capacity, the small tube sheets being easier to manufacture and less costly than is a single large tube sheet.

Kraupa Sept. 23, 1975 STEAM GENERATOR [75] inventor: Werner Kraupa,Erlangen,

Germany [73] Assignee: Siemens Aktiengesellschaft, Munich,

Germany 22 Filed: Aug. 29, 1973 211 App]. No.: 392,524

[30] Foreign Application Priority Data Sept. 8, 1972 Germany 2244207 [52] U.S. Cl 122/32; 127/34 [51] Int. Cl F22b 1/06 [58] Field of Search 122/32, 33, 34, 483

[56] References Cited UNITED STATES PATENTS 2,845,906 8/1958 Gram, Jr 122/32 3,251,404 5/1966 Dickinson. 122/32 V 3,682,140 8/1972 Roftler 122/34 Primary Examiner-Kenneth W. Sprague Attorney, Agent, or FirmKenyon & Kenyon Reilly Carr & Chapin [57] ABSTRACT A steam generator includes inverted U-shaped tubes having vertical legs and formed into two nests each having inlet and outlet groups of legs with the return portions of all of the tubes positioned in the lower portion of an enclosure having a steam outlet and in which a water separator for the generated steam is positioned above the tube return portions. Individual casings all connecting with the enclosures lower portion, extended downwardly therefrom and individually encase the respective groups of legs individually, the ends of each group of legs being mounted in a tube sheet separate from the others. Each of these tube sheets is provided with a separate manifold for the tubes of the group of legs mounted by that tube sheet. This construction permits the use of tube sheets which are individually small while permitting the heat exchanger to be designed to have a relatively high steam generated capacity, the small tube sheets being easier to manufacture and less costly than is a single large tube sheet.

5 Claims, N0 Drawings .I l STEAM GENERATOR BACKGROUND OE'THE mveurlou.

Steam for'power purposes is obtained in the'case of ya nuclear reactor using a pressurized-water coolant, by

circulating the coolant through a steam generator'having a Casing enclosing nest of inverted U-shaped tubes having vertical legs with their lower ends mounted in a tube sheet connected with the lower portion of th'e'casthe coolant through the tubes of the tube nest, this circulation ordinarily being aided by pumping equipment.

The tube sheet serves to mount the tubesof the tube nest and confine the pressure of the generating: steam, and it is exposed to the heat of the coolant which is hot; and when it enters the inlet ends of the tubes, it is hotter than when it leaves their outlet ends, causing severe thermal stressing. The tube sheet must be made of material that is highly corrosion resistent. The tube sheet requires drilling to form the holes in which the ends of the tubes are mounted. It follows that for these and other reasons, the manufacture of a tube sheet involves a very substantial manufacturing cost, this cost increasing disproportionately as the size of the tube sheet increases.

Pressurized-water coolant reactors are being made with increasing output ratings, this demanding larger steam generators requiring larger sizes of tube sheets. An effort to reduce tube sheet cost by using a multiplicity of smaller steam generators for one reactor, is impractical because of the cost of the pipe lines required for connecting a multiplicity of steam generators, the extra space required by multiplicities of steam generators and other factors which wipe out any savings that might be effected in this manner.

SUMMARY OF THE INVENTION An object of the present invention is to provide a steam generator of the type described, having a large capacity, but constructed in such a manner as to reduce such tube sheet expense.

According to the invention, the inverted U-shaped tubes are formed into two tube nests each having an inlet and outlet groups of the vertical legs with the return or looped portions of all of the tubes in the lower portion of an enclosure having the steam outlet and containing the water separator. This results in four groups of the legs depending from the enclosure, and these each are encased by individual casings having top ends all connecting with the enclosures lower portion and extending downwardly therefrom, each casing being only large enough to encase its one group of the legs, and the ends of each group of legs being mounted in a tube sheet separate from the others. Although four tube sheets are involved, each tube sheet is small and therefore much less expensive than would be the single large tube sheet that would be required by the prior art design. Each of these four tube sheets is provided with a separate manifold for the tubes of its group of legs.

This results in two inlet manifolds and two outlet manifolds, but these may connect with the reactor-coolant pipes via short and therefore inexpensive branching With this new construction, it is possible to make-all four of the tube sheets in an identical manner, involving larger scale production possibilities permitting further reduction in their manufacturing costin addition-to their small size. Furthermore, each tube sheet operates at substantially the same temperature throughout its extent, avoiding non-uniform thermal'stressing, ther mal stressing being less harmful in any event because of the small size of the tube sheets.

Each; tube sheet has below iit'a hemispherical manifoldand since each manifold functions only as an inlet or outlet manifold as the ease may be, it does'not require the partition necessitated by the prior art design requirement thatone enclosure must function both as an inlet and outle't manifold for the tube nest legs mounted in the tube sheet.

I "The enclosure above the two tube nests may be made as large as in the case of the prior'art steam generator ofcomparable capacity, providing plenty of room for the water separator which, incidentally, may comprise a number of components. i

DESCRIPTION OF THE DRAWING The accompanying drawing schematically illustrates the new construction in perspective.

DETAILED DESCRIPTION OF THE INVENTION Having reference to the above drawing, the steam generator has a casing section 1 contoured in a doubly bifurcated manner forming downwardly converging, approximately frustoconical connections 2 through 5, which are identical with each other. Thus the section 1 provides four identical circular openings 8 which all lie in the same plane, and at its top the section forms a large cylindrical opening 9 which is connected to a cylindrical shell 10 which, in effect, represents the corresponding portion of the prior art steam generator. Four identical cylindrical casings 12 through 15 extend downwardly from the openings 2 through 5, these all being identical and each provided at its lower end with the tube sheet 16 of small size, these tube sheets all being identical. The two tube nests are indicated by broken lines at 17 and 18, the tubes of the tube nests being parallel to each other and individually encased by the cylindrical casings 12 through 15, the casings in each instance having diameters only sufficient to encase the groups of legs individually.

The bottoms of the tube sheets 16 in each instance are enclosed by a hemispherical manifold 20 having coolant pipe connections 21 in the form of stubs which may be connected to the reactors coolant lines via short branch pipes. As shown by the drawing, the left hand pair of elements function as the inlet portion of the new steam generator, the coolant flow being indicated by the arrow 22, the right hand side being the outlet portion with the outlet coolant flow being indicated by the arrow 25. The casings l4 and 15 on the right hand side are provided with feed water input inlets of which one is generally indicated at 150, the feed water rising in the casings l4 and 15 and flowing over into the casings 12 and 13 until a proper water level up in the large enclosure 10 is obtained. The generated steam rises upwardly to the steam dome 28 formed by the part and is discharged via the steam output 29. Within the large portion 10 the usual water separators 27 are generally indicated by broken lines.

It can be seen that there are no particular manufacturing problems involved by this construction. The identical small tube sheets 16 can be relatively easily manufactured and obviously at a reduced cost. the collective manufacturing cost of the four tube sheets being substantially less than would be required for a large tube sheet having, for example, the diameter of the enclosure 10. Collectively the small tube sheets weigh only 1/2 the weight of such a larger tube sheet.

What is claimed is:

l. A steam generator including inverted U-shaped tubes having return portions and vertical legs depending from said portions, casing means enclosing said legs, an enclosure having a lower portion with which said means upwardly connects and having a steam outlet, and means for conducting heating fluid through said tubes; wherein the improvement comprises said tubes being formed into two nests each having inlet and outlet groups of said legs arranged in a doubly bifurcated manner with the return portions of all of the tubes in the lower portion of said enclosure, said casing means being formed by individual casings all connecting with the enclosures said lower portion and extending downwardly therefrom and respectively encasing said groups of legs individually, a tube sheet in each of said casings, the ends of each group of legs being mounted in the tube sheet in its encasing casing separate from the others, and a separate manifold for each of said tube sheets and the tubes of its group of the legs, the enclosures said lower portion being contoured in a doubly bifurcated manner forming downwardly converging and approximately frusto-conical connections with said individual casings.

2. The steam generator of claim 1 in which said tube sheets are all substantially identical with each other.

3. The steam generator of claim 1 in which said manifolds are each substantially hemispherical and has an opening for the heating fluid.

4. The steam generator of claim 1 in which said enclosure contains a water separator above the return portions of said nests of tubes, for separating water from the generated steam.

5. The steam generator of claim 4 in which said enclosure is substantially cylindrical with said lower portion connecting with said casings. 

1. A steam generator including inverted U-shaped tubes having return portions and vertical legs depending from said portions, casing means enclosing said legs, an enclosure having a lower portion with which said means upwardly connects and having a steam outlet, and means for conducting heating fluid through said tubes; wherein the improvement comprises said tubes being formed into two nests each having inlet and outlet groups of said legs arranged in a doubly bifurcated manner with the return portions of all of the tubes in the lower portion of said enclosure, said casing means being formed by individual casings all connecting with the enclosure''s said lower portion and extending downwardly therefrom and respectively encasing said groups of legs individually, a tube sheet in each of said casings, the ends of each group of legs being mounted in the tube sheet in its encasing casing separate from the others, and a separate manifold for each of said tube sheets and the tubes of its group of the legs, the enclosure''s said lower portion being contoured in a doubly bifurcated manner forming downwardly converging and approximately frusto-conical connections with said individual casings.
 2. The steam generator of claim 1 in which said tube sheets are all substantially identical with each other.
 3. The steam generator of claim 1 in which said manifolds are each substantially hemispherical and has an opening for the heating fluid.
 4. The steam generator of claim 1 in which said enclosure contains a water separator above the return portions of said nests of tubes, for separating water from the generated steam.
 5. The steam generator of claim 4 in which said enclosure is substantially cylindrical with said lower portion connecting with said casings. 